This invention relates to a spiral tube aerator for waste water aeration, and includes a shaft rotatably driven at one end by a motor and carrying a mixing member at an end opposite thereof, a blower supplies air to outlets of the mixing member through an axial air bore or channel of the shaft, and with the mixing member immersed in waste water, air or oxygen is conveyed into the waste water which bubbles upwardly to provide aeration thereof.
It is conventional to use spiral tube aerators to convey air or oxygen into waste water. Normally, the conventional rotating shaft of a spiral tube aerator carries a mixing member designed as a multi-winged propeller or a helical propeller. The mixing member causes high acceleration of the water directly obliquely downward therefrom which creates suction to draw air through the bore of the shaft. Thus, as the mixing member is rotated by rotating the shaft, the air is distributed in fine bubbles and a portion of the oxygen thereof is dissolved in the waste water for aeration purposes. In order to obtain efficient aeration and a relatively large length of ascent of the small air bubbles of the mixing members to the surface of the waste water, the mixing member is normally arranged as far below the water surface as is possible. However, when introducing air into the bore of the shaft, it is difficult to overcome the high water pressure at the depth of the mixing member immersion. Thus, it is necessary in such conventional waste water aerators to provide a motor which consumes high electrical power/energy which in turn is simply not cost effective. Generally the air so introduced into the bore of the spiral tube aerator shaft is approximately 35 m.sup.3 /kWh.
There are, of course, spiral tube aerators in which low-pressure compressors supply pressurized air to the air bore or channel of the shaft leading to the mixing member (German laid open Patent Application 32 08 025). In this case the over-pressure in relation to atmosphere amounts to ca. 11.2 mbar. The overpressure is intended to provide extreme depth of operation of the spiral tube aerator and, of course, particularly a depth as great as possible for the immersion of the mixing member thereof. Air is introduced at low energy levels under a slight over-pressure so as to enable the mixing member to be submerged somewhat deeper into the waste water than the first type of aerators described herein.
It is also known to provide a mixing member for fluids in which the wings thereof are provided on the shaft carrying the mixing member within an enveloping jacket (German Utility Model 74 11 389). As the shaft rotates, the wings thereof form an axial blower and, therefore, only low air-pressure is necessary to serve as prepressure to create suction during the rotation of the mixing member. Furthermore, the number of revolutions of the shaft which are turned to the density of the water are far too low to build up significant air pressure along the wings.